BEIJING (Reuters) - China's military called on Tuesday for unity and loyalty to the ruling Communist Party after one of its most senior former officers was accused of corruption, the highest-ranking official to date felled in a battle against pervasive graft.

Xu Caihou, who retired as vice chairman of the powerful Central Military Commission last year and from the Communist Party's decision-making Politburo in 2012, was also expelled from the party and will be court-martialled.

President Xi Jinping heads the Central Military Commission, which controls the 2.3 million-strong armed forces, the world's largest, and has repeatedly reminded them to be loyal to the party.

In a front page commentary, the military's official People's Liberation Army Daily called on its forces to "resolutely endorse the correct decision of the party's centre ... the Central Military Commission and Chairman Xi".

"Our military is an armed bloc which carries out the ruling party's political mission, and must have high standards when it comes to building a clean party and government," it said, on a day that also marks 93 years since the party was founded.

"The military holds the barrels of the guns, and cannot give hiding space to corrupt elements. Absolute loyalty, absolute purity and absolute reliability are the political demands of the party for the military," the commentary said.

Xi has made weeding out corruption in the military a top goal. It also comes as Xi steps up efforts to modernize forces that are projecting power across the disputed waters of the East and South China Seas, though it has not fought a war in decades.

The party has struggled to contain public anger at a seemingly endless stream of corruption scandals, particularly when officials are seen as abusing their posts to amass wealth.

China stepped up a crackdown on rampant corruption in the military in the late 1990s, banning the PLA from engaging in business. But the military has engaged in commercial dealings in recent years due to a lack of checks and balances, sources say.

The buying and selling of military positions has also been an open secret but Chinese media have generally avoided the topic. It is difficult to assess how widespread the problem is.

For officers who paid bribes to be promoted, corruption is seen as a means of making a return on investment. Examples of graft include leasing military-owned land to private business, selling military licence plates, illegally occupying military apartments or taking kickbacks when buying food or equipment.